The present application claims priority under 35 U.S.C. xc2xa7119 of French Patent Application No. FR 02/06980 filed on Jun. 6, 2002.
1. Field of the Invention
The invention relates to the cold forming of parts from blanks, particularly metal blanks. It applies in particular to blanks made of press sintered material.
2. Discussion of Background Information
xe2x80x9cCold formingxe2x80x9d is to be understood as meaning deformation of the metal of the blank at ambient temperature or in the semi-hot state (up to a temperature of 300 to 500xc2x0 C. depending on the metal of the blank), i.e., below its melting point.
A distinction should be drawn between cold forming by revolution rolling (xe2x80x9crollingxe2x80x9d for short), which uses rotary tools or the equivalent, as opposed to other methods of cold forming such as machining, drop forging, stamping or extension.
There are several configurations for forming by rolling:
external forming of the blank, using a tool, the blank being held in some other way, or alternatively using two or more tools distributed uniformly around the external periphery of the blank;
internal forming of a hollow blank, using at least one internal tool and at least one external tool, or an external support which turns with the blank.
Furthermore, the blank is often driven by the tool or tools, but can also be driven separately, in synchronism or otherwise.
Mastering the position of the tools with respect to the blank is a particularly tricky operation. Use is generally made of hydraulic (ram) or mechanical (screw-nut) position control. However, it has become apparent that the known control techniques were not always satisfactory, particularly in the case of blanks made of press sintered material, as will be seen.
The present invention improves the situation.
The invention thus provides for a method of cold forming by rolling a blank made of press sintered material. In the method, at least one tool of predetermined peripheral geometry is brought close to the blank, so that the tool can then be rolled over the blank, urging the one towards the other.
According to one aspect of the invention, this method comprises, after a phase (a) of approaching the blank, a penetration phase (b), with:
(bn) at least one phase of rolling under roughly constant load, as far as a chosen position, this load, the chosen position, and the corresponding number of passes being determined so as to control the surface densification and the dimensions of the rolled part.
According to another aspect of the invention, after a phase (a) of approaching the blank, a penetration phase (b) is provided, with:
(b1) at least one phase in which the rolling load increases, bounded by a maximum value of this rolling load.
The phase (bn) of rolling under roughly constant load can then take place, as appropriate.
The invention also provides for a method of cold forming a blank made of press sintered material, comprising moving at least one tool towards the blank and subjecting the blank to rolling under a roughly constant load for a number of passes until the at least one tool reaches a chosen position, wherein at least one of, the chosen position, the roughly constant load, and the corresponding number of passes, is determined so as to control a surface densification and at least one dimension of the rolled blank.
The at least one tool may have a predetermined peripheral geometry. The method may further comprise rolling the at least one tool over the blank. The method may further comprise urging the at least one tool and the blank towards one another. Each of the chosen position, the roughly constant load, and the corresponding number of passes may be determined so as to control a surface densification and at least one dimension of the rolled blank. The method may further comprise controlling the roughly constant load. The method may further comprise, before the subjecting, rolling the blank with an increasing load. The method may further comprise, before the subjecting, rolling the blank with an increasing load up to a maximum value. The method may further comprise, before the subjecting, rolling the blank with an increasing load up to the roughly constant load. The method may further comprise, before the subjecting, rolling the blank with a controlled increasing load up to the roughly constant load. The method may further comprise, before the subjecting, rolling the blank with a controlled increasing load. The method may further comprise, before the subjecting, rolling the blank with an increasing load that is determined according to a critical law which tends to bring a load progression close to an experimentally determined permissible limit value that takes account of geometric and mechanical properties of the blank.
The subjecting may comprise maintaining the roughly constant load below a limit value defined with respect to a threshold at which the press sintered blank deteriorates. The subjecting may comprise maintaining the roughly constant load below a limit value defined with respect to a threshold at which the at least one tool deteriorates. The subjecting may comprise maintaining the roughly constant load at a value close enough to a limit value to avoid excessive work hardening while at the same time minimizing a rolling time.
The moving and the subjecting may be repeated after a direction of rotation of the at least one tool has been reversed. The method may further comprise subjecting the blank to finish rolling. The finish rolling may comprise maintaining the roughly constant relative positions of the blank and the at least one tool for a chosen length of time.
The at least one tool may comprise peripheral profile that is at least one of roughly circular and generally cylindrical. The blank may comprise a preformed part. The preformed part may comprise teeth. The preformed part may comprise a ring. The ring may comprise a bearing ring. The at least one tool may comprise teeth. The at least one tool may comprise a uniform external periphery.
The method may further comprise controlling the moving and the subjecting via a program. The moving and the subjecting may occur on a numerically controlled machine. The subjecting may comprise first subjecting the blank to rolling under a roughly constant load for a number of passes until the at least one tool reaches a first chosen position, and second subjecting the blank to rolling under a roughly constant load for a number of passes until the at least one tool reaches a second chosen position. The subjecting may comprise first subjecting the blank to rolling under a load for a number of passes until the at least one tool reaches a first chosen position, and second subjecting the blank to rolling under a roughly constant load for a number of passes until the at least one tool reaches a second chosen position.
The invention also provides for a method of cold forming a press sintered material part, comprising moving at least one tool towards the part and subjecting the part to controlled rolling under a roughly constant load for a number of passes until the at least one tool reaches a chosen position, wherein the chosen position, the roughly constant load, and the corresponding number of passes, is determined so as to control a surface densification and at least one dimension of the part being rolled.
The invention still further provides for a method of cold forming a press sintered material part, comprising moving at least one tool towards the part, subjecting the part to a first rolling under a first controlled load for a number of passes until the at least one tool reaches a first chosen position, and subjecting the part to a second rolling under a roughly constant second controlled load for a number of passes until the at least one tool reaches a second chosen position, wherein the first chosen position, the second chosen position, the roughly constant load, and the corresponding number of passes, is determined so as to control a surface densification and at least one dimension of the part being rolled.